Re: [PATCH v6 03/13] mm/demotion: Return error on write to numa_demotion sysfs

From: Ying Huang <ying.huang@intel.com>
To: Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>,
	linux-mm@kvack.org, akpm@linux-foundation.org
Cc: Wei Xu <weixugc@google.com>, Greg Thelen <gthelen@google.com>,
	Yang Shi <shy828301@gmail.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Tim C Chen <tim.c.chen@intel.com>,
	Brice Goglin <brice.goglin@gmail.com>,
	Michal Hocko <mhocko@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Hesham Almatary <hesham.almatary@huawei.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Alistair Popple <apopple@nvidia.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Feng Tang <feng.tang@intel.com>,
	Jagdish Gediya <jvgediya@linux.ibm.com>,
	Baolin Wang <baolin.wang@linux.alibaba.com>,
	David Rientjes <rientjes@google.com>
Subject: Re: [PATCH v6 03/13] mm/demotion: Return error on write to numa_demotion sysfs
Date: Mon, 13 Jun 2022 13:33:52 +0800	[thread overview]
Message-ID: <33b42a802a07721c639db99ed208ed43f743bb37.camel@intel.com> (raw)
In-Reply-To: <9da3c6ef-ba0d-6229-2188-0956222b04f1@linux.ibm.com>

On Mon, 2022-06-13 at 09:05 +0530, Aneesh Kumar K V wrote:
> On 6/13/22 8:56 AM, Ying Huang wrote:
> > On Fri, 2022-06-10 at 19:22 +0530, Aneesh Kumar K.V wrote:
> > > With CONFIG_MIGRATION disabled return EINVAL on write.
> > > 
> > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> > > ---
> > >   mm/memory-tiers.c | 3 +++
> > >   1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> > > index 9c6b40d7e0bf..c3123a457d90 100644
> > > --- a/mm/memory-tiers.c
> > > +++ b/mm/memory-tiers.c
> > > @@ -105,6 +105,9 @@ static ssize_t numa_demotion_enabled_store(struct kobject *kobj,
> > >   {
> > >   	ssize_t ret;
> > >   
> > > 
> > > 
> > > +	if (!IS_ENABLED(CONFIG_MIGRATION))
> > > +		return -EINVAL;
> > > +
> > 
> > How about enclose numa_demotion_enabled_xxx related code with CONFIG_MIGRATION?
> > 
> 
> IIUC there is a desire to use IS_ENABLED() in the kernel instead of 
> #ifdef since that helps in more compile time checks. Because there are 
> no dead codes during compile now with IS_ENABLED().

IS_ENABLED() is used to reduce usage of "#ifdef" in ".c" file,
especially inside a function.  We have good build test coverage with
0Day now.

To avoid code size inflate, it's better to use #ifdef CONFIG_MIGRATION.

> W.r.t leaving the sysfs file visible even when CONFIG_MIGRATION is 
> disabled, I was thinking it gives better visibility into numa_demotion 
> status. I could switch to hide numa_demotion file if that is desirable.
> 
> > >   	ret = kstrtobool(buf, &numa_demotion_enabled);
> > >   	if (ret)
> > >   		return ret;
> > 

Best Regards,
Huang, Ying